1. Field of the Invention
The present invention relates to the processing of audio data, and more particularly, to an apparatus and method of encoding audio data and an apparatus and method of decoding encoded audio data, in which the bitrate of encoded audio data may be adjusted, and even when the audio data included in a bitstream to be decoded is encoded audio data of some of the layers of the encoded audio data, the audio data of all of the layers may be recovered.
2. Description of the Related Art
Bit sliced arithmetic coding (BSAC), which has been proposed by the applicant of the present invention, is a coding technique providing FGS (Fine Grain Scalability). In addition, BSAC is an audio compressing technique adopted as a standard by a moving picture experts group (MPEG)-4. BSAC is detailed in Korean Patent Publication No. 261253. Unlike BSAC, the advanced audio coding (AAC) technique does not provide FGS.
When an encoder that uses the AAC encodes audio data, it can encode only audio data in some of the frequency bands of the audio data and transmit the encoded audio data to a decoder.
In this case, a spectral band replication (SBR) technique may be considered to recover the audio data in all frequency bands from the audio data in only certain encoded frequency bands that have been encoded using the ACC. In other words, the encoder that uses the AAC generates and encodes SBR data having information about audio data in frequency bands other than the certain encoded frequency bands and transmits the SBR data to the decoder together with the encoded audio data in the certain encoded frequency bands. The decoder can recover the original audio data by inferring the audio data in the frequency bands other than the certain encoded frequency bands. As such, the MC and SBR techniques can be combined together.
Meanwhile, when an encoder that uses the BSAC encodes audio data, in contrast with the encoder that uses the MC, the encoder that uses the BSAC can generate a base layer and at least one enhancement layer by dividing the audio data according to frequency bands, encode all of the layers of the audio data, and transmit only the audio data of selected encoded layers that include the base layer to a decoder. Here, since the selected layers are variable, the bit rate of the audio data encoded using the BSAC may be adjusted.
In contrast with the easy combination of the ACC and SBR techniques, combining the BSAC and SBR techniques incurs certain difficulties. That is, some of the encoded audio data layers to be transmitted to the decoder may vary on a case by case basis, and thus, different SBR data should be generated for all possible cases.
There is a demand for a scheme that is able to recover encoded audio data having layers using SBR data that is identical, regardless of the selected layers of the audio data to be transmitted to a decoder.